The present invention relates to a water meter which can be used in a variety of nominal width pipelines without adjustment.
Water meters, which operate according to the Woltmann principle are well known in the prior art. Some representative water meters are disclosed in WO 91/04462, DE 841 952, DE 37 32 703 A1, U.S. Pat. No. 3,811,323 and U.S. Pat. No. 3,999,432. Water meters need to be installed in pipe lines of differing nominal widths. In order not to have to manufacture water meters for each nominal width pipeline a measuring insert to adapt the water meter to a range of structural sizes can be provided. Nominal widths are combined into groups of nominal widths, in which like measuring inserts, i.e. measuring inserts identical in structural size and of identical construction, are employed. Thereby the production costs for the measuring inserts can be lowered.
According to prior art, the measuring inserts of one nominal width-group must be calibrated for each rated value. This entails various disadvantages. For one, the costs of calibrating are increased since equipment parts adapted to the different nominal widths are required. For another, servicing the measuring inserts is difficult since the operators of the meters frequently state incorrect nominal widths in the event of a service request. The service technician in this case either brings to the site of installation an incorrect measuring insert, i.e. one calibrated to another nominal width or, preventively, carries along several measuring inserts calibrated to various nominal widths of the nominal width-group. A further disadvantage is that warehousing costs increase for each group of nominal widths as a greater number of calibrated measuring inserts must be kept in readiness.
The present invention addresses the problem of eliminating the above listed disadvantages of prior art.
This problem is solved according to the present invention with water meters with a housing with aligned inflow region, outflow region, and a measuring insert disposed coaxially between them. The housing is identical for all nominal widths of the nominal width-group. Mounted inside the housing is a measuring annulus having a coaxially disposed an upstream holding means and a downstream holding means. Between the holding means an impeller wheel is rotatably supported, whose vanes project into an annular channel formed between the holding means and the measuring annulus. The inner contour of the inflow region and the outer contour of the upstream holding means are shaped such that, independent of the nominal width of the connected pipe line, in the annular channel directly in front of the impeller wheel a substantially rectangular velocity distribution is obtained. This results in stream lines directed substantially parallel to the wall of the annular channel, allowing accurate measurement of fluid flow.
Stated in general terms, the solution of this problem lies in that, independently of the nominal width of the connected pipe line, in the water meters at the annular channel directly in front of the impeller wheel a substantially rectangular velocity distribution is obtained with stream lines aligned substantially parallel to the wall of the annular channel. This results in flow conditions at identical flow rates in different sized pipes are substantially identical. Therefore only it is necessary to calibrate the measuring insert for one nominal width of the nominal width-group. It is the possible, without changing the adjustment and without repeated calibration, to use the water meter in each nominal width of the nominal width-group.
In one embodiment of the present invention the upstream holding means comprises a substantially perpendicular face of stream incidence, which transitions into a cylindrical or slightly conical diverging shell surface, which forms the inner wall of the annular channel, with the transition being shaped such that directly in front of the impeller wheel a substantially rectangular velocity distribution is obtained.
This formation contributes to the fact that even in the case of the smallest or the smaller nominal widths of the nominal width-group not only identical integrated flow velocities are present in front of the impeller wheel but also that uniform flow conditions obtain from which results a uniform flow against the vanes of the impeller wheel when viewed over the cross section of the annular channel.
The primary aspect of the present invention is to provide a water meter which can be used in a number of different sized pipelines without additional calibration.
Other aspects of this invention will appear from the following description and appended claims, reference being made to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.
The present invention relates to water meters for the installation in pipe lines of the group of nominal widths from 50 to 100 mm. Part of this nominal width-group are the nominal widths conventionally and commonly used in practice of 50, 80 and 100 mm as well as, if appropriate, an additional fourth nominal width of 65 mm.